Vacuum pumps may be fitted to road vehicles with gasoline or diesel engines. Typically, the vacuum pump is driven by a camshaft of the engine. Therefore, in most vehicles the vacuum pump is mounted to an upper region of the engine. But other configurations where the vacuum pump is mounted to a lower region of the engine are known. In general, two different construction types of vacuum pumps are known, one is the type incorporating a movable piston, and the other is vane pump. Nowadays, vane pumps are frequently utilized.
A vane pump of the aforementioned type typically comprises a casing having a cavity and a movable member arranged for rotation inside the cavity, wherein the cavity is provided with an inlet and an outlet and a movable member is movable to draw fluid into the cavity through the inlet and out of the cavity through the outlet so as to induce a reduction in pressure at the inlet. The inlet is connectable to a consumer such as a brake booster or the like. The outlet normally is connected to the engine's crankcase. Furthermore, the vacuum pumps of the aforementioned type also comprise an oil supply conduit for supplying oil from the engines lubrication circuit to the vacuum pump and a check valve having a check valve body arranged in the oil supply conduit.
Such a vacuum pump, for example, is disclosed in WO 2007/116 216. The disclosed vacuum pump comprises a check valve which is arranged in an oil supply conduit to prevent the flow of oil to the cavity during periods when the pump is not operating. When the pump is not operating it is possible that oil drains by means of gravity into the cavity or is drawn into the gravity by a residual vacuum inside the cavity. The check valve known from WO 2007/116 216 A1 prevents oil from flowing into the cavity.
However, it can also happen that during operation too much oil is supplied to the cavity. Excess oil inside the cavity leads to inefficient operation of the vacuum pump and increases the vacuum pump power consumption. Therefore, arrangements have been developed which meter or dose the oil flow to the cavity. For example, EP 1 972 785 B1 suggests providing a slidably supported valve member inside the check valve which is slidable in a direction perpendicular to a rotational axis of the shaft of the vacuum pump. The slidably supported valve member is arranged in such a way that rotational speed of the shaft the oil supply conduit is more open so that more oil is supplied to the cavity.
From EP 0 406 800 B1 a vacuum vane pump is known which incorporates dosing the oil flow dependent on rotational speed of a vane pump. The disclosed vane pump comprises a first groove in fluid connection with an oil supply conduit and arranged adjacent to the shaft of the vane pump inside the housing, a through bore perpendicular to the rotational axis of the shaft provided in the shaft and a second groove in fluid communication with the cavity and arranged adjacent to the shaft of the vane pump inside the housing. The through bore is arranged in such a way that on rotation it connects the first with the second groove thus allowing oil flow from the oil supply conduit to the cavity. Further, EP 0 406 800 B1 discloses one or two spherical valve elements inside the through bore to measure or dose the oil flow in such a way that e.g. on every rotation an amount of oil equal to the volume of the through bore is supplied to the cavity.